Saw-tooth wave generation



F eb.-

S. H. M. DODINGTON SAW-TOOTH WAVE GENERATION Filed July l8,"l942 INVENTOR SVEN H.M.DODINGTON BY ATTORNEY Patented Feb. 25, 1947 SAW-TOOTH ViAVE GENERATIQN Sven H. M. Dodington, Forest Hills, N. Y., as-

. signor to Federal Telephone and Radio Cor-, :poration, a corporation of Delaware Application July 18, 1942, Serial No. 451,455"

This invention relates to high frequency sawtooth wave generation and to multivibrator means for producing high frequency voltage surges therefor.

One of the objects of this invention is to provide means for generating saw-tooth waves at high speed wherein the ratio of the wave front or fly-back time interval to the major slope time interval of the waves is maintained small.

Another object of this invention is to provide means for generating saw-tooth waves wherein the wave fronts and major slopes thereof are'substantially linear:

Still anotherobject of this invention is to provide a four-stage multivibrator capable of operating at high frequencies.

The above and other objects of this invention are accomplished by a system including a fourstage multivibrator, a constant current control device and a positive feed-back circuit. The multivibrator generates high frequency voltage surges which I use to charge a capacitance. The constant current control device controls the discharge of the capacitanceto produce saw-tooth'waves the slopes of which approach linearity. The positive feed-back circuit I use to feed back a part of the saw-tooth wave voltage to correct fornonlinearity.

Two-stage multivibrators are limited to low frequenc operation because continued oscillation requires high plate load constants. Inaccordance with my invention, I overcome this frequency limiting feature of prior multivibrators by providing two additional stages of amplificae tion to boost the instantaneous voltage of the initial stage. This insuresrmultivibrator operation :at higher and higher frequencies as the plate load constants are reduced. The plate load constants of the first and last stages of my four-stage multivibrator may be reduced several times in comparison with the plate load constants of known two-stage multivibrators, and therebyincrease greatly the speed of oscillation. Thus, where the highest satisfactory frequency operation of existing two-stage multivibrators is about 500 to 800 kilocycles, the-four-stage multivibrator of my invention may be made to operate satisfactory at frequencies as high a 4000 kilocycles.

For high frequency operation, I find that the stray capacities of the tube components and associated wiring of the circuit is sufficient for the purpose of saw-tooth generation without the provision of a special condenser. A constant current control device such as a pentode tube may be adjusted by varying the screen grid potential 7 Claims. (01. 250-36) controlled bythe constant current device.

thereof so as to control the discharge of the capacitance to produce a desired major slope for saw-tooth wave generation. This adjustment of the screen grid potential of the pentode tube may, together with the unusually low plate load constants of the first and fourth stages of' my multivibrator determine the general shape and the frequency of the saw-toothwaves.

In order to insure substantially linear slopes in the saw-tooth waves, I provide in accordance with my invention a; positive feed-back of saw-tooth Wave voltage, fed back through suitable resistances from the grid-cathode electrodes of a final amplifier stage to the constant current pentode to tubes V2, V3 and V4, respectively. The output of the triode tubeVl is connected to a constant current control pentode V5 whichin turn may be connected to an amplifier stage having a tetrode tube V6. The output of 'the amplifier tubeVB may be applied to a sweeplcircuit of acathode ray tube or for any other purpose desired. 1

In saw-tooth wave generation, it is customary to provide the multivibrator or other voltage surge source with a condenser which is charged by the multivibrator circuit and the discharge thereof As hereinbefore suggested;I have discovered that for high frequency operation, the stray capacities of the tube components and the associated wiring of the circuit is sufficient to' provide the requisite capacitance for saw-tooth generation. This 'capacitance is indicated as a condenser C bybroken lines in association with the cathode output of the initial stage VI. v

Operation of my circuit will become apparent as the detailed description proceeds. The output of tubeVl is resistance coupled to'theinput of tube V2 by a plate load resistor I I! having inherent stray capacitance I3, and by a capacitance l l. The output of tube V2 is resistancei coupled to the input of the tube V3 by plateload resistor l5 and by capacitance l6. The outputof tube V3 is coupled to the input of the tube'V4 by plate i may thus state that the output of tube VI is coupled by a plate load resistance Ill, a high frequency amplifier 20, and a capacitance I8 to the input of the tube V4. The output of tube V4 is resistance coupled back to the gridinput of tube V I 7 V! by a plate load resistance 22 having stray capacitance 23. This is the feed-back feature characteristic of a multivibrator.

Suppose a slight increase in plate current ocours in tube VI. This increase in plate current, will reduce the plate voltage of tube VI and will therefore, set up through amplifier 20 a more negative voltage on the grid of tube V4. This in turn will cause a reduction in plate current of tube V4 with a corresponding increase-in its plate voltage. A more positive voltagewill, therefore, be induced on the grid of tube VI causing still further increase in its plate current. This process is cumulative and the plate current in tube V2 will die down to zero while that in tube VI will build up to some final value. The capacitance C will now be charged very nearly to the plate voltage of VI, and VI will no longer draw current. It may now be said that the charging of the capacitance C is complete.

The discharge cycle of the capacitance C now occurs, the discharge being controlled at a steady rate by the pentode V thus producing a linear change in voltage across capacitance C. Meanwhile, due, to the fact that VI is no longer drawing current, there is no voltage drop across the resistance I0, and V4 is consequently drawing fullcurrent thereby maintainin the grid of VI. beyond cut-off. However, as the'capacitance C loses its charge through the pentodeV5, a point is reached where the cathode voltage of VI is low enough to start a fiow of plate current in VI. This produces a drop across the plate load resistor I0 of tube VI therebyinitiating the charging operation of eapaoitanceC-J Heretofore, values of plate load resistors I0 and 22 had to be relatively large in multivibrator circuits in order to maintain oscillation. As

hereinbefore suggested, this fact has heretofore necessarily limited multivibrator circuits to .relatively low frequency operation. The values of 5 the plate load resistors II] and I2 may be re- I multivibrator may be in the order of 100 and 1,000 ohms respectively. These low time constants are made possible by the amplification efiected by the two tubes V2 and V3 since they boost the instantaneous plate voltage of tube VI, thereby compensating 'for the reduction of amplification produced by' the aforementioned reduction of plate resistors.

The output 28 from the tube VI-is coupled to the constant control tube V5 and the tube V6,

' sisters 32 and 34, the latter being connected-to ground, to cathode-screen terminal 38 of tube V5. The resistors 32 and 34 are so chosen in relation to a grid to groundresistor 36 that a small part of the output voltage of the tube V6 is fed back and applied across the cathode and grid terminals 38 and 39 of the pentode tube V5. This feed-back voltage is indicated by the waves 42. Cathode resistors 32 and 34 maybe in the order of ohms and '5 ohms respectively, and the resistor, 36 of one megohm, although these values may be varied to get more or less correction as may be desired.

This feed-back voltage has the eifectof producing a somewhat quicker discharge of the capacitance C at a time when the voltage on the. grid of tube Vfi is at a minimum thereby correcting for the deviation of waves 4| from linearity. My circuit not only provides enough feedback to compensate for the non-linearity occurring in the saw-tooth waves 40, but may in addition provide feed-back sufficient to compensate for non-linearity effects produced bythe output tube V6. Thus, the feed-back is made to overcorrect the non-linearity of waves 4I resulting in nonsaw-tooth waves having substantially linear t slopes can be produced thereby. While I have shown and described one particular embodiment of the invention, it will be understood that the embodiment is to be regarded as illustrative of the inventiononly andnot as restricting the appended claims. q

What I claim is:

l. A high frequency saw-tooth generator comprising a four-stage multivibrator, one of said stages having a triode tube, another of said stages having a tetrode tube, the output of the tetrode tube being applied on the grid of the triode, a capacitance chargeable by said triode tube, and a constant current control device to control the discharge of said capacitance in the order of a saw-tooth wave.

2. A high frequency saw-tooth generator comprising a four-stage multivibrator, each stage having grid and plate leads, said stage being connected in circuit with the plate lead of the preceding stage coupled to a grid lead of the next succeeding stage and the plate lead of the last stage being connected to the grid lead of the first stage, a capacitance chargeable by said multivibrato-r, and'aconstant current control device to control the discharge of said capacitance in the order of a saw-tooth wave.

3. A high frequency saw-tooth generator comprising-a four-stage multivibrator, each stage having, grid andplate leads, said-stage -jbeing connected in circuit with the plate lead of the preceding stage coupled to a grid lead of the next succeeding stage and the plate lead of the last stage connected to the grid lead of the first stage, a capacitance chargeable by said multivibrator, low plate load resistors for the first and last stages to effect high frequency oscillation, the second and third stages operating as amplifiers to boost the amplitude of the oscillating surges to insure continued high frequency operation, and means to control the rate of discharge of said capacitance.

4. A high frequency saw-tooth generator comprising a four-stage multivibrator, each stage having grid and plate leads, said stages being connected in circuit with the plate lead of the preceding stage coupled to a grid lead of the next succeeding stage and the plate lead of the last stage connected to the grid lead of the first stage, a capacitance chargeable by said multivibrator, low plate load resistors for the first and last stages to effect high frequency oscillation, the second and third stages operating as amplifiers to boost the amplitude of the oscillating impulses to insure continued high frequency operation; means to control the discharge of said capacitance in the order of a saw-tooth wave, an amplifier stage to amplify the saw-tooth wave output, and a feedback path between said amplifier stage and said constant current device to return a part of the wave voltage to correct for non-linearity of the wave slope.

5. A multivibrator comprising four stages, one stage having a triode tube and another having tetrode tube, the plate of said tetrode tube being connected to the grid of said triode tube, the plate load resistors of said triode and said one tetrode being selected low to efiect high frequency oscillation, and the other two of said stages being arranged to amplify the oscillating surges to insure continued high frequency operation.

6. A multivibrator comprising four stages, each stage having grid and plate leads, said stages being connected in circuit with the plate lead of the preceding stage coupled to a grid lead of the next succeeding stage and the plate lead of the last stage being connected to the grid lead of the first stage.

7. A multivibrator comprising four stages, each stage having grid and plate leads, said stages being connected in circuit With the plate lead of the preceding stage coupled to a grid lead of the next suceeding stage and the plate lead of the last stage being connected to the grid leadof the first stage, low plate resistors for the first and last stages to effect high frequency oscillation, and the second and third stages operating as amplifiers to boost the amplitude of the oscillating surges to insure continued high frequency operation.

SVEN H. M. DODINGTON.

REFERENCES CITED The following references are of record in th file of this patent: V

UNITED STATES PATENTS Number Name Date 2,207,940 Norton July 16, 1940 1,978,461 Hoover et al Oct. 30, 1934 2,114,938 Puckle Apr. 19, 1938 2,155,210 Young Apr. 18, 1941 2,232,076 Newsam Feb. 18, 1941 2,237,425 Geiger Apr. 8, 1941 

